1. Field of the Invention
The present invention relates to a method and an apparatus for controlling a communication system. More particularly, the present invention relates to a method and an apparatus for flow control between a Packet Data Convergence Protocol (PDCP) layer and a Radio Link Control (RLC) layer in an evolved Node B (eNB) of a communication system.
2. Description of the Related Art
FIG. 1 is a schematic block diagram of a communication system, which may be, for example, a Long Term Evolution (LTE) communication system as shown according to the related art.
Referring to FIG. 1, a communication system includes an evolved Node B (eNB) 100, a Serving Gate Way (S-GW) 110, and a core network 120. The S-GW 110 and the core network 120 do not perform an operation actually related to the present invention, so a detailed description thereof will be omitted here.
The eNB 100 includes Radio Link Control (RLC) layers 102, 104, and 106 corresponding to sectors included in a serving cell, in which the eNB 100 provides a service, and a Packet Data Convergence Protocol (PDCP) layer 108 controlling the RLC layers 102, 104, and 106. Although the serving cell includes three sectors in the example shown in FIG. 1, the serving cell may include more or fewer sectors than the three sectors. Although not shown in the drawings, each of the RLC layers 102, 104, and 106 and the PDCP layer 108 has a buffer.
The PDCP layer 108 stores Service Data Units (SDUs) in an RLC Acknowledge Mode (AM) in its own buffer (PDCP buffer) in order to forward the PDCP SDUs at the time of handover or Radio Resource Control (RRC) reconfiguration. At this time, the PDCP layer 108 may store SDUs in an Unacknowledgement Mode (UM) also in the PDCP buffer for performance improvement. The PDCP layer 108 operates a discard timer simultaneously with the storing operation, and transfers PDCP Packet Data Units (PDUs) to a lower layer after a processing, such as Robust Header Compression (RoHC), in order to improve the performance of a radio link in which packet loss may frequently occur. Thereafter, when receiving an Acknowledgement (ACK) signal notifying that the PDUs have been normally received from the lower layer before the discard timer expires, the PDCP layer 108 discards corresponding SDUs from the PDCP buffer.
A buffer (RLC buffer) of each of the RLC layers 102, 104, and 106 has been designed to accommodate traffic of one sector of the serving cell, and the PDCP buffer has been designed to accommodate traffic of all the sectors included in the serving cell. Therefore, the size of the PDCP buffer is larger than the size of the RLC buffer. However, the PDCP buffer does not store PDUs in view of traffic, but stores SDUs before the processing in view of call processing, that is, only in order to forward them when a call is connected to another eNB. Therefore, when an overflow temporarily occurs in the RLC buffer, it is impossible to prevent the packet loss due to the overflow in the RLC buffer even when the PDCP buffer of the relatively large size is empty.
Furthermore, in the method of the related art notifying that the PDUs having been transmitted to the lower layer have been normally received, the lower layer transmits, 1:1, an ACK or a Non-Acknowledgement (NACK) signal corresponding to each of the normally received PDUs to the PDCP layer the baseband selection unit 108. Therefore, the 1:1 transmission of the corresponding ACK signal may degrade the efficiency when there are multiple PDUs, to which the ACK signal should be transmitted.
Therefore, a need exists for a method and an apparatus for flow control between an RLC layer and a PDCP layer in a communication system